Most sheaths that have been designed for carrying knives are intended to permit the knife to be pulled quickly from the sheath. In some instances, straps with snap fasteners have been provided to secure the knife in the sheath against accidental dislodgement. In knives and sheaths designed for use by divers the sheath has frequently been provided with a flexible, stretchable rubber or rubber-like loop that can be stretched over the handle to secure it in place.
While such means for securing a knife in a sheath are adequate for most purposes, they have limitations, especially when the knife is worn in unusual environmental situations such as occur when the knife is carried by divers.
Divers have use for a knife and sheath combination in which the knife will remain securely in the sheath during normal movements of the diver, but which can be quickly and easily removed by the diver when he wishes. The sheath construction most commonly used by divers has been a sheath with a rubber-like ring. That construction, while securely holding the knife in the sheath during normal movement of the diver, does not permit easy removal of the knife. The rubber ring has to be stretched and distended by the diver. Since the diver works underwater and frequently in the dark, it may not always be easy to free the knife from the rubber ring and then remove it from the sheath.